the-tcpdump-group/tcpdump
GitHub: the-tcpdump-group/tcpdump
经典的命令行网络数据包捕获与分析工具，用于实时监控网络流量和排查网络问题。
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# TCPDUMP 4.x.y 由 [The Tcpdump Group](https://www.tcpdump.org/) 开发
**如需报告安全问题，请发送电子邮件至 security@tcpdump.org。**
如需报告错误和其他问题、贡献补丁、请求功能、提供一般反馈等，请参阅 tcpdump 源代码树根目录下的[贡献指南](CONTRIBUTING.md)。
可通过以下方式使用匿名 Git：
```
https://github.com/the-tcpdump-group/tcpdump.git
```
本目录包含 tcpdump 的源代码，这是一个用于网络监控和数据采集的工具。
在过去几年中，得益于互联网社区的卓越贡献，tcpdump 得到了稳步改进（只需浏览[变更日志](CHANGES)即可了解）。我们感谢所有的投入。
### 支持的平台
在许多操作系统中，tcpdump 以原生包或端口的形式提供，这简化了更新安装和长期维护。然而，原生包的版本有时会落后一些，若要尝试更新的快照，则需要从源代码编译 tcpdump。
tcpdump 至少可以在以下平台上编译和运行：
过去，tcpdump 肯定或很可能可以在以下平台上运行：
### 对 libpcap 的依赖
tcpdump 使用 libpcap，这是一个用于用户级数据包捕获的系统独立接口。如果您的操作系统未提供 libpcap，或者提供的 libpcap 不支持 libpcap 1.0 或更高版本的 API，则在构建 tcpdump 之前，您必须先获取并构建 libpcap。
一旦构建了 libpcap（安装它，或者确保它位于 `../libpcap` 中），您就可以按照[安装说明](INSTALL.md)中的步骤构建 tcpdump。
### tcpdump 的起源
该程序大致基于 SMI 的“etherfind”，尽管目前未保留任何 etherfind 代码。它最初由 Van Jacobson 编写，作为一个正在进行的研究项目的一部分，旨在调查和改进 TCP 及互联网网关的性能。最初取自 Sun etherfind 的程序部分后来由 LBL 的 Steven McCanne 重写。为了确保 tcpdump 中不存在任何专有代码的痕迹，Steve 根据手册条目中给出的规范编写了这些部分，并未访问 tcpdump 或 etherfind 的源代码。
```
formerly from Lawrence Berkeley National Laboratory
Network Research Group
ftp://ftp.ee.lbl.gov/old/tcpdump.tar.Z (3.4)
```
### 另请参阅
Richard Stevens 在他的书 *《TCP/IP 详解 卷1》* 中对互联网协议进行了精彩的论述。如果您想了解更多关于 tcpdump 的知识以及如何解释其输出，请阅读这本书。
tcpdump 用户可能会发现另一个有用的工具是 [tcpslice](https://github.com/the-tcpdump-group/tcpslice)。
这是一个可用于提取 tcpdump 二进制跟踪文件部分的程序。
### Steve McCanne、Craig Leres 和 Van Jacobson 撰写的原始 LBL README
```
This directory also contains some short awk programs intended as
examples of ways to reduce tcpdump data when you're tracking
particular network problems:
send-ack.awk
Simplifies the tcpdump trace for an ftp (or other unidirectional
tcp transfer). Since we assume that one host only sends and
the other only acks, all address information is left off and
we just note if the packet is a "send" or an "ack".
There is one output line per line of the original trace.
Field 1 is the packet time in decimal seconds, relative
to the start of the conversation. Field 2 is delta-time
from last packet. Field 3 is packet type/direction.
"Send" means data going from sender to receiver, "ack"
means an ack going from the receiver to the sender. A
preceding "*" indicates that the data is a retransmission.
A preceding "-" indicates a hole in the sequence space
(i.e., missing packet(s)), a "#" means an odd-size (not max
seg size) packet. Field 4 has the packet flags
(same format as raw trace). Field 5 is the sequence
number (start seq. num for sender, next expected seq number
for acks). The number in parens following an ack is
the delta-time from the first send of the packet to the
ack. A number in parens following a send is the
delta-time from the first send of the packet to the
current send (on duplicate packets only). Duplicate
sends or acks have a number in square brackets showing
the number of duplicates so far.
Here is a short sample from near the start of an ftp:
3.00 0.20 send . 512
3.20 0.20 ack . 1024 (0.20)
3.20 0.00 send P 1024
3.40 0.20 ack . 1536 (0.20)
3.80 0.40 * send . 0 (3.80) [2]
3.82 0.02 * ack . 1536 (0.62) [2]
Three seconds into the conversation, bytes 512 through 1023
were sent. 200ms later they were acked. Shortly thereafter
bytes 1024-1535 were sent and again acked after 200ms.
Then, for no apparent reason, 0-511 is retransmitted, 3.8
seconds after its initial send (the round trip time for this
ftp was 1sec, +-500ms). Since the receiver is expecting
1536, 1536 is re-acked when 0 arrives.
packetdat.awk
Computes chunk summary data for an ftp (or similar
unidirectional tcp transfer). [A "chunk" refers to
a chunk of the sequence space -- essentially the packet
sequence number divided by the max segment size.]
A summary line is printed showing the number of chunks,
the number of packets it took to send that many chunks
(if there are no lost or duplicated packets, the number
of packets should equal the number of chunks) and the
number of acks.
Following the summary line is one line of information
per chunk. The line contains eight fields:
1 - the chunk number
2 - the start sequence number for this chunk
3 - time of first send
4 - time of last send
5 - time of first ack
6 - time of last ack
7 - number of times chunk was sent
8 - number of times chunk was acked
(all times are in decimal seconds, relative to the start
of the conversation.)
As an example, here is the first part of the output for
an ftp trace:
# 134 chunks. 536 packets sent. 508 acks.
1 1 0.00 5.80 0.20 0.20 4 1
2 513 0.28 6.20 0.40 0.40 4 1
3 1025 1.16 6.32 1.20 1.20 4 1
4 1561 1.86 15.00 2.00 2.00 6 1
5 2049 2.16 15.44 2.20 2.20 5 1
6 2585 2.64 16.44 2.80 2.80 5 1
7 3073 3.00 16.66 3.20 3.20 4 1
8 3609 3.20 17.24 3.40 5.82 4 11
9 4097 6.02 6.58 6.20 6.80 2 5
This says that 134 chunks were transferred (about 70K
since the average packet size was 512 bytes). It took
536 packets to transfer the data (i.e., on the average
each chunk was transmitted four times). Looking at,
say, chunk 4, we see it represents the 512 bytes of
sequence space from 1561 to 2048. It was first sent
1.86 seconds into the conversation. It was last
sent 15 seconds into the conversation and was sent
a total of 6 times (i.e., it was retransmitted every
2 seconds on the average). It was acked once, 140ms
after it first arrived.
stime.awk
atime.awk
Output one line per send or ack, respectively, in the form
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